yellow backs 

Teeth that are white on the front, but yellow on the back.

Person A: I just finished brushing my teeth!
Person B: Did you remember to bush the back?
Person A: Nope!
Person B: Okay, but don't come crying to me in someone finds out that you have yellow backs.

yellow backs by ChameleonDragon March 10, 2018

yellow fronted brown backs 

A pair of ageing and rarely laundered scads.

"I took my grandma to see Tom Jones the other night. She got carried away and slung her Yellow Fronted Brown Backs at the poor sod..."

yellow fronted brown backs by J Biscuit August 30, 2007

have a yellow streak down your back 

to be a coward, to be cowardly

You obviously have a yellow streak down your back.

have a yellow streak down your back by Light Joker May 6, 2006

Yellowback 

Typically found in the UK, yellowbacks are so named for their fluorescent or “High Visibility” jackets and can be seen “Working”, usually for a local council, on many, if not most, roads in the country holding up traffic whilst supposedly there to start digging it up at some point to make sure your taxes all get spent for the financial year.

Usually middle aged, bald (either naturally or by choice), heavily tattooed and overweight, yellowbacks like to smoke (invariably roll up’s), drink tea and shout- which is not usually necessary as their power tools will rarely be turned on.

Due to Health and safety legislation, it can take up to twenty yellowbacks to perform even the simplest of tasks such as turning round the “Stop” and “Go” signs or sitting in gritting lorries eating sausage rolls. Despite the unisex “Staff working at rear” warning signs on such vehicles, nobody has ever seen a female yellowback.

Bob: "Them roadworks have been going on every day for weeks!"

Phil: "It's the council's fault! They're too tight to pay the yellowbacks night wages!"

Yellowback by UpYourKilt August 30, 2011